KYIV, Ukrain — Russian drones battered the Ukrainian port city of Odesa and glide bombs hit Zaporizhzhia, local authorities said Tuesday, as the Kremlin again warned that negotiators are unlikely to obtain a swift breakthrough in peace talks on the war.

Ukrainian, British, French and U.S. officials are due to meet in London on today to discuss the war.

Anticipation is building over whether diplomatic efforts can stop more than three years of fighting since Russia’s full-scale invasion of its neighbor. Hostility has run deep since Russia invaded and illegally annexed Ukraine’s Crimean Peninsula in 2014.

Retired Lt. Gen. Keith Kellogg, U.S. President Donald Trump’s envoy for Ukraine and Russia, will represent Washington in peace discussions with Ukrainian and European officials this week in London, the U.S. State Department said Tuesday.

U.S. Secretary of State Marco Rubio won’t attend because of a scheduling issue, according to spokeswoman Tammy Bruce.

“They want diplomacy to work,” Bruce said of both Trump and Rubio.

Trump said last week that negotiations were “coming to a head,” and insisted that neither side is “playing” him in his push to end the war. That came after Rubio suggested that the U.S. might soon back away from negotiations if they don’t progress.

Rubio has suggested today’s meeting could be decisive in determining whether the Trump administration continues its involvement.

But Kremlin spokesman Dmitry Peskov cautioned that “the settlement issue is so complex that it would be wrong to put some tight limits to it and try to set some short time frame for a settlement, a viable settlement — it would be a thankless task.”

President Volodymyr Zelenskyy said Tuesday that Ukraine’s delegation heading to the U.K. has a mandate to discuss only an unconditional or partial ceasefire with Russia.

“We are also ready to commit that after a ceasefire, we’re prepared to sit down for talks in any format,” he told reporters at a media briefing.

Zelenskyy added that Ukraine would only believe Russia is serious about peace once it shows results.

Amid ongoing talks, discussions about potential territorial concessions by Ukraine, particularly over Crimea, have recently intensified as a possible bargaining chip in negotiations.

But Zelenskyy reiterated that Ukraine will never recognize the occupation of Crimea or other territories, saying such concessions are incompatible with the country’s constitution. “There is nothing to talk about — it is our land,” he said.

Putin’s foreign affairs adviser, Yuri Ushakov, said that Trump envoy Steve Witkoff was expected to visit Moscow again this week.

Western analysts say Moscow is in no rush to conclude peace talks, because it has battlefield momentum and wants to capture more Ukrainian land.

Russia has effectively rejected a U.S. proposal for an immediate and full 30-day halt in the fighting by imposing far-reaching conditions.

Odesa came under a “massive attack” by Russian drones overnight, wounding at least three people, the head of the regional administration, Oleh Kiper, wrote on his Telegram page.

A residential building in a densely populated urban area, civilian infrastructure and an educational facility were hit, he said.

Later Tuesday, Russia hit the southern city of Zaporizhzhia with two aerial glide bombs.

The attack killed a 69-year-old woman and wounded 24 people, including four children, according to regional governor Ivan Fedorov.

Zelenskyy said in a Telegram post that his earlier offer of a ceasefire covering civilian sites still stands.

“Russia needs to be seriously prepared to talk about this,” Zelenskyy said. “There are no obstacles on the Ukrainian side and there will be none.”